Process control maps to design an ultra-high strength-ductile steel

Abstract

Steel with 2.4-2.5 GPa tensile strength and elongation to fracture of 4.8-5.7%, is produced by designing a novel heat treatment identical to quenching and tempering, in less than a few minutes. Since addition of Si to Fe-Mn steel promotes the austenite stabilisation by carbon enrichment, the elongation to fracture of 0.6C-1.6Si-1.2Mn (wt-%) steel treated by different quenching and partitioning (Q&P) routes is improved. Results demonstrated by process control maps give a good overview of the final microconstituents. By using higher partitioning temperatures, the tempering of martensite, stabilisation of austenite and improvement of the mechanical properties, could effectively be accelerated. This approach results in significant time and cost reduction which makes this heat treatment attractive for industries.

Kinetics of Carbon Enrichment in Austenite during Partitioning Stage Studied via In-Situ Synchrotron XRD

“…Additionally, to illustrate these constituents graphically, an optical micrograph of the specimen partitioned at 500 °C for 20 s and tint-etched using the Lepera method [ 58 ] is shown as one example in Figure 8 . With this method of etching, (i) tempered martensite is shown in a blue scheme color [ 59 ], (ii) slightly tempered fresh martensite and ferritic bainite are shown in beige/light brown colors [ 60 ], and (iii) retained austenite remains white.…”

High-performance reality of 55SiCrV spring steel processed by the rapid-induction heat treatment

“…However, with common rapid induction heating and cooling followed by tempering treatment at 400 °C-450 °C temperature, the strength of this kind of steel can barely reach 2000 MPa. The strength could be further increased by lowering the tempering temperature, but at the cost of reducing ductility and toughness [3][4][5]. Hence, the commercial medium carbon Si-Cr martensitic steels could not satisfy the next generation SSS, and it is necessary to develop new designs for SSSs with acceptable ultrahigh strength and ductility.…”